1. Field of the Invention
The present invention relates to a color image reading apparatus used for document reading of a digital copying machine and an input terminal of a personal computer and a document size detecting method in the color image reading apparatus.
2. Description of the Related Art
In a color image reading apparatus which is used for a digital copying machine or a personal computer and reads optical image information from a document using a color charge coupled device (hereinafter abbreviated to CCD), a document size detecting device for forward-scanning a document at the time of pre-scanning, deciding whether the document is a color document or a monochromatic document, at the time of backward scanning, detecting the document size on the decision level based on the obtained decision result, thereby preventing a misdetection is disclosed in Japanese Patent Publication 6-59351. However, this conventional document size detecting device detects first the document size at the time of backward scanning, so that the pre-scanning time for detecting the document size is prolonged and it is an obstacle to speeding up the image reading operation.
Furthermore, in a color image reading apparatus using a color CCD sensor, conventionally, regardless of a color document or a monochromatic document, an apparatus for detecting the document size by the color CCD sensor at the time of pre-scanning for detecting the document size is known. However, in this conventional apparatus, even for a monochromatic document the size of which can be originally detected in a short-time, the same detection time as that at the time of detection of the color document size is required to detect the document size. Therefore, in a monochromatic document, the pre-scanning time is wasted and speeding up of the reading operation is disturbed.
Therefore, in a color image reading apparatus using a color CCD sensor, it is desired to surely detect the document size regardless of a color document or a monochromatic document and shorten the pre-scanning time to speed up the image reading operation.